1. Field of the Invention
The present invention relates to a blade for a lancet and, more particularly, relates to a lancet blade designed for reducing the amount of pain inflicted when being used to draw blood from a patient for diagnostic testing.
2. Background Description
A lancet is a device commonly used in hospitals, doctors offices and homes to pierce a patient's flesh to draw capillary blood for diagnostic testing. Conventional lancets consist of a shank portion having at a distal end a blade or spike, which is sharp and adapted to pierce the patient's skin so to sever capillaries and provide blood for testing. Since the blade or spike is sharp, some lancets are provided with a removable shield for protectively covering the sharp edge or point of the lancet's blade or spike when not in use to protect the patient and users from inadvertent skin puncture.
FIG. 1 is a perspective view of a conventional lancet assembly 10 described in U.S. Pat. No. 4,577,630 (Nitzsche et al), which is assigned to Becton, Dickinson and Company. Lancet assembly 10 includes a handle portion 11, a spike 12 extending outwardly from a distal end 13 and a removable shield 14 adapted to mate with spike 12 when the lancet is not in use and protect users from accidental puncture. Spike 12 in lancet assembly 10 can also be replaced with a conventional lancet blade, like that shown in FIG. 2.
As shown in FIG. 2, conventional lancet blade 20 has an included angle .theta. of 60.degree., a blade width A of 1.1 mm, a blade length B of 1.85 mm and a shear length C of 0.635 mm. In addition, blade 20 has a shear percentage of 34%, wherein: ##EQU1## An example of a conventional lancet assembly for holding blade 20, is described in U.S. Pat. No. 4,616,649 (Burns), assigned to Becton, Dickinson and Company, which is similar to the 6356 Lancet sold by Becton, Dickinson and Company.
A problem with the lancets described above is that during penetration the blade or spike initially cuts but then tears sensitive nerve endings where the puncture wound is made in a finger, which causes a significant amount of pain to the patient. When using blade 20 shown in FIG. 2, the skin is cut by a shearing action over the shear length C of the blade. However, after the shearing portion of the blade has been fully inserted into the puncture wound, the blade continues to enter the skin without any cutting action being performed by the blade. Since the thickness of blade 20 continues to increase beyond the sheared portion, additional blade thickness is forced into the puncture wound thus causing tearing of the skin, which results in increased pain to the patient. Such pain to the patient is very severe since the nerve endings in the finger are very sensitive.